FIG. 1 shows an exemplary depiction of a computing system 100. According to the computing system design of FIG. 1, a central processing unit (CPU) 101 (such as a microprocessor) is used to execute instructions that effectively perform the software routines that are executed by the computing system 100. The computing system also includes a graphics controller (which may also be referred to as a display controller) 104 that provides digital information (e.g., in the form of bytes of digital data or “words” of digital data that are wider than 8 bits) to a display unit 105.
The display unit 105 is designed to transform the stream of digital information provided by the graphics controller 104 into orchestrated analog signals that, when applied to a display device (such as a liquid crystal display device or a thin film transistor display device), result in the appearance of visual subject matter (e.g., a graphical user interface (GUI)) on the display unit 105. The graphics controller 104 is typically designed to perform numerically intensive functions (e.g., that are used to display fluid motions on the display device) so as to offload from the CPU 101 the burden of performing these functions.
In the embodiment of FIG. 1, a memory controller and bridge unit 102 is coupled to both the graphics controller 104 and the CPU 101. The memory controller and bridge unit 102 may be implemented, for example, with a pair of semiconductor chips (e.g., a memory controller chip; and, a bridge chip) or a single semiconductor chip. The bridge portion of the memory controller and bridge unit 102 effectively acts as a gateway that allows other “I/O components” 1071 through 107N (e.g., a disk drive, a CD read only memory (ROM), a networking interface, a diskette drive, a card interface, etc.) to store information into (or retrieve information from) the system memory 103. Typically, the I/O components share a bus 106 (e.g., a PCI bus) to which the bridge portion of the memory controller and bridge unit 102 is also coupled.
The bus 106 provides an efficient mechanism for sending information between the system memory 103 and the I/O components 1071 through 107N because each I/O component uses common signal wiring from which the bus 106 is constructed. The bridge portion of the memory controller and bridge unit 102 may translate between a pair of buses (e.g., bus 106 and a second bus (not shown in FIG. 1) that acts as a third input/output port to the memory controller portion of the memory controller and bridge unit 102); or, may simply provide a third/input output port to the memory controller portion of the memory controller and bridge unit 102.
The memory controller portion of the memory controller and bridge unit 102 effectively controls the reading and writing signaling activity (e.g., addressing signals) applied to the system memory 103. Here, as both the CPU 101 and the various I/O components 1071 through 107N may invoke the services of the system memory 103 (e.g., in the case of the CPU 101, for reading instructions or reading/writing data; or, in the case of an I/O component, for forwarding data that will be worked upon by the computing system's software), the memory controller portion of the memory controller and bridge unit 102 may effectively arbitrate or otherwise resolve the contention for the system memory's data storage services that may arise between the various I/O components 1071 through 1071 and the CPU 101. To the extent that the graphics controller 104 invokes use of the system memory 103, the memory controller portion of the memory controller and bridge unit 102 may also arbitrate its demands as well.
It is important to point out that other computing system embodiments are possible; and, as such, the term computing system, computer and the like are not to be construed as automatically limited to the exemplary architecture that has been depicted in FIG. 1. Some exemplary alternative computing system embodiments might entail: 1) coupling the graphics controller 104 to the processor 101 rather than the memory controller and bridge unit 102; 2) not having a graphics controller 104 (e.g., such that the numerically intensive graphical calculations are performed by the CPU 101); 3) not having an external (off-chip) cache 108 relative to the CPU 101; etc. Note that the combination of the CPU 101, memory controller 102 and system memory 103 (and display controller 104 and external cache 108 if they are implemented) may be referred to as the processing core 109 of the computing system 109.
Mobile computing systems such as laptop computers, notebook computers, handheld devices (e.g., personal digital assistants, cellphones, IEEE 802.11 based devices, etc.) are often battery powered; and, as such, power consumption is a matter of concern. Typically, the less power consumed by a mobile computing system, the longer the life of the battery that powers the computing system. Often, mobile computing systems are built with a “sleep mode” and/or a “hibernation mode”. Either of these modes substantially shut down the activity of the computing system so that battery power is conserved.
In “sleep mode” the computing system's “appendages” outside the processing core 109 (e.g., its display unit 105, one or more I/O components 1071, through 1071) are shut down while its volatile memory within the processing core 19 (e.g., the external cache 108, the system memory 103, etc.) is kept awake (e.g., by continuing to clock/refresh and/or otherwise apply power to the cache and the system memory 103). The CPU 101 may also shut down various internal units so that the processing of application software effectively ceases. Sleep mode allows the system to conserve battery power consumption (because of the shut down of the appendages and internal CPU units) and also allows the computing system to rapidly awake because its volatile memory was never shut down.
In “hibernation mode” the contents of the volatile memory (e.g., cache and system memory) are first stored to non volatile memory (e.g., a disk drive); and then, the entire system is effectively shut down. Here, typically, greater power savings are realized as compared to the sleep mode because the volatile memory units are shut down. However, it takes longer for the system to return from hibernation mode to its original, normal, active state because the “state” of the system software at the time hibernation mode was entered (as represented by the matter that was transferred from volatile to non volatile memory) needs to be “reloaded” back into volatile memory (e.g., by reading the state data from the disk drive and re-storing it back to its original locations in cache and system memory 103).
Unfortunately, during either sleep mode or hibernation mode, the utility of a mobile computing system is effectively non existent because the CPU (being shut down) lacks the ability to execute a variety of instructions. That is, useful software routines (such as email retrieval, downloading information from the internet, etc.) cannot be executed.